It has been heretofore known to apply polyolefin layers to both surfaces of paper prepared for photographic purposes. In many cases, the polyolefin layer which is between the paper support and the light sensitive photographic emulsion has pigments added thereto, such as titanium dioxide in order to render the polyolefin layer white in appearance. This also increases the reflectivity of the polyolefin surface and improves the quality of the resulting photograph. A problem that exists with such substrates employed in the photographic art is that the sharpness of the resulting image formed in the light sensitive layers is not as high as is desirable when very high quality images are needed, for example, in professional applications. This is generally true because it is not possible to include sufficiently high percentages of pigment material in the polyolefin coatings to achieve the opacity and reflectivity necessary for high sharpness quality images.
In order to overcome this problem, the prior art suggests that a layer of gelatin containing titanium dioxide particles be interposed between one of the polyolefin layers and the light sensitive photographic emulsion. British Patent Specification No. 1,551,258 suggests a photographic paper coated on both sides with polyethylene and coated on one polyethylene surface with a mixture of gelatin, colloidal silica, and particles of titanium dioxide, baryta or (non-colloidal) silica having an average particle size within the range of 0.1 to 5 microns and optionally an anionic surface active agent.
U.S. Pat. No. 4,558,002, issued Dec. 10, 1985, teaches a photographic paper having such a structure wherein the layer intermediate to the polyolefin layer and the light sensitive layer is a hydrophilic colloid layer containing a dye or pigment that is not decolored during photographic processing and a white pigment present in the hydrophilic colloid layer in an amount not less than 30% by volume.
U.S. Pat. No. 4,755,454 suggests a structure similar to the two preceding discussed references wherein the hydrophilic colloid layer contains a white pigment present in an amount of at least 68 percent by weight.
In order to improve sharpness in color paper, it is possible to place a reflective layer between the emulsion and RC layer. However, a significant degradation of the sharpness can still be caused by the backscatter of light from the reflective layer. To minimize this backscatter, it is possible to put an antihalation layer between the reflective layer and the silver halide emulsion layer or to add an absorber dye into the emulsion layer.
However, while this improves sharpness, it is at the cost of a great loss in sensitivity. It is also possible to coat an antihalation layer below the reflective layer (U.S. Pat. No. 4,563,406; EP 337 490). This method provides improved sharpness without such a significant loss in speed. However, this method requires that two extra layers be coated onto the paper support.